Method for forming spacers using silicon nitride film for spacer-defined multiple patterning

ABSTRACT

A method of forming spacers for spacer-defined multiple pattering (SDMP), includes: depositing a pattern transfer film by PEALD on the entire patterned surface of a template using halogenated silane as a precursor and nitrogen as a reactant at a temperature of 200° C. or less, which pattern transfer film is a silicon nitride film; dry-etching the template using a fluorocarbon as an etchant, and thereby selectively removing a portion of the pattern transfer film formed on a top of a core material and a horizontal portion of the pattern transfer film while leaving the core material and a vertical portion of the pattern transfer film as a vertical spacer, wherein a top of the vertical spacer is substantially flat; and dry-etching the core material, whereby the template has a surface patterned by the vertical spacer on a underlying layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 15/048,422, filed Feb. 19, 2016, the disclosure of which is herein incorporated by reference in its entirety. The applicant/inventors herein explicitly rescind and retract any prior disclaimers or disavowals made in any parent, child or related prosecution history with regard to any subject matter supported by the present application.

BACKGROUND Field of the Invention

The present invention relates generally to a method for fabricating a layer structure constituted by a dielectric film containing a Si—N bond in a trench formed in an upper surface of a substrate.

Related Art

In manufacturing processes of large-scale integrated circuits (LSIs), there are several processes for forming sidewalls in trenches. The sidewalls are used as spacers or used for blocking etching of a structure from side surfaces of trenches. Conventionally, the sidewalls were formed by forming a conformal film on surfaces of trenches, and then removing portions thereof formed on an upper surface in which the trenches were formed and portions formed on bottom surfaces of the trenches by asymmetrical etching. However, when such a formation method is used, over-etching is required in order to remove footing of sidewalls in which the thickness of the sidewalls increases near and at the bottom, forming a slope. Over-etching causes etching of an underlying layer and causes damage to a layer structure.

Any discussion of problems and solutions in relation to the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion was known at the time the invention was made.

SUMMARY

The embodiments disclosed herein include various aspects and technological features. In one focused aspect, among other aspects, in some embodiments, a method of forming spacers for spacer-defined multiple pattering (SDMP), comprises: (i) providing a template having a surface patterned by a mandrel formed on an underlying layer in a reaction space; (ii) depositing a pattern transfer film by plasma-enhanced atomic layer deposition (PEALD) on the entire patterned surface of the template using halogenated silane as a precursor and nitrogen as a reactant at a temperature of 200° C. or less, said pattern transfer film being a silicon nitride film; (iii) dry-etching the template whose entire upper surface is covered with the pattern transfer film using a fluorocarbon as an etchant, and thereby selectively removing a portion of the pattern transfer film formed on a top of the mandrel and a horizontal portion of the pattern transfer film while leaving the mandrel as a core material and a vertical portion of the pattern transfer film as a vertical spacer, wherein a top of the vertical spacer is substantially flat; and (iv) dry-etching the core material, whereby the template has a surface patterned by the vertical spacer on the underlying layer.

In some embodiments, the mandrel is constituted by a carbon-based material.

In some embodiments, in step (ii), PEALD uses is a capacitively coupled plasma (CCP) and is conducted by applying 300 W or less of RF power in the reaction space.

In some embodiments, in step (ii), the pattern transfer film has a conformality of 80% to 100%.

In some embodiments, in step (iii), the fluorocarbon is CHF₃, C₄F₈, or CF₄.

In some embodiments, in step (iv), the core material is etched using Ar/O₂ or O₂ as an etchant.

In some embodiments, the pattern transfer film is a single silicon nitride film deposited under same conditions.

In some embodiments, the method further comprises (v) dry-etching the underlying layer using the vertical spacer as a mask.

In some embodiments, SDMP is space-defined quadruple patterning (SDQP), wherein after step (iv) before step (v), steps (ii) to (iv) are repeated.

For purposes of summarizing aspects of the invention and the advantages achieved over the related art, certain objects and advantages of the invention are described in this disclosure. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

Further aspects, features and advantages of this invention will become apparent from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will now be described with reference to the drawings of preferred embodiments which are intended to illustrate and not to limit the invention. The drawings are greatly simplified for illustrative purposes and are not necessarily to scale.

FIG. 1A is a schematic representation of a PEALD (plasma-enhanced atomic layer deposition) apparatus for depositing a protective film usable in an embodiment of the present invention.

FIG. 1B illustrates a schematic representation of a precursor supply system using a flow-pass system (FPS) usable in an embodiment of the present invention.

FIG. 2 is a flowchart illustrating steps of fabricating a layer structure according to an embodiment of the present invention.

FIG. 3 is a flowchart illustrating steps of fabricating a layer structure according to another embodiment of the present invention.

FIG. 4 is a flowchart illustrating steps of fabricating a layer structure according to still another embodiment of the present invention.

FIG. 5 is a flowchart illustrating steps of fabricating a layer structure according to yet another embodiment of the present invention.

FIG. 6 is a flowchart illustrating steps of fabricating a layer structure according to a different embodiment of the present invention.

FIG. 7 is a graph showing the relationship between RF power and wet etch rate of a film formed on a top surface and that of a film formed on sidewalls of a trench, showing a threshold (reference) RF power, according to an embodiment of the present invention.

FIG. 8 shows Scanning Electron Microscope (SEM) photographs of cross-sectional views of silicon nitride films formed according to embodiments of the present invention.

FIG. 9 shows a Scanning Electron Microscope (SEM) photograph of a cross-sectional view of a silicon nitride film formed according to an embodiment of the present invention.

FIG. 10 illustrates a cross-sectional view of a silicon nitride film formed according to an embodiment of the present invention.

FIG. 11 illustrates a cross-sectional view of a silicon nitride film formed according to another embodiment of the present invention.

FIG. 12 is a graph showing the relationship between RF power and Si—N peak intensity [au] of a SiN film according to an embodiment of the present invention.

FIG. 13 is a graph showing the relationship between RF power and density [g/cm³] of a SiN film according to an embodiment of the present invention.

FIG. 14 is a graph showing a general relationship between plasma density and wet etch rate of a film formed on a top surface and that of a film formed on sidewalls of a trench according to an embodiment of the present invention.

FIG. 15 shows a Scanning Electron Microscope (SEM) photograph of a cross-sectional view of conventional spacers constituted by silicon oxide.

FIG. 16 is a graph showing the relationship between deposition power and dry etching rate of SiN film according to an embodiment of the present invention.

FIG. 17 illustrates cross-sectional views of a silicon nitride film, wherein (a) illustrates high-ion dose areas in dark gray when the film is deposited, (b) illustrates ion irradiation areas in dark gray when the film is subjected to dry etching, and (c) illustrates an etched structure according to an embodiment of the present invention.

FIG. 18 shows a Scanning Electron Microscope (SEM) photograph of cross-sectional views of a silicon nitride film deposited on a resist pattern in (a) and spacers formed by etching the film in (b) according to an embodiment of the present invention.

FIG. 19 is a schematic representation of pattern transfer and target etching (steps (a) to (i)) using spacer-defined double patterning (SDDP) according to an embodiment of the present invention.

FIG. 20 is a schematic representation of double patterning (steps (a) to (c)) and quadruple patterning (steps (c) to (e)) according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

In this disclosure, “gas” may include vaporized solid and/or liquid and may be constituted by a single gas or a mixture of gases. In this disclosure, a process gas introduced to a reaction chamber through a showerhead may be comprised of, consist essentially of, or consist of a precursor gas and an additive gas. The precursor gas and the additive gas are typically introduced as a mixed gas or separately to a reaction space. The precursor gas can be introduced with a carrier gas such as a noble gas. The additive gas may be comprised of, consist essentially of, or consist of a reactant gas and a dilution gas such as a noble gas. The reactant gas and the dilution gas may be introduced as a mixed gas or separately to the reaction space. A precursor may be comprised of two or more precursors, and a reactant gas may be comprised of two or more reactant gases. The precursor is a gas chemisorbed on a substrate and typically containing a metalloid or metal element which constitutes a main structure of a matrix of a dielectric film, and the reactant gas for deposition is a gas reacting with the precursor chemisorbed on a substrate when the gas is excited to fix an atomic layer or monolayer on the substrate. “Chemisorption” refers to chemical saturation adsorption. A gas other than the process gas, i.e., a gas introduced without passing through the showerhead, may be used for, e.g., sealing the reaction space, which includes a seal gas such as a noble gas. In some embodiments, “film” refers to a layer continuously extending in a direction perpendicular to a thickness direction substantially without pinholes to cover an entire target or concerned surface, or simply a layer covering a target or concerned surface. In some embodiments, “layer” refers to a structure having a certain thickness formed on a surface or a synonym of film or a non-film structure. A film or layer may be constituted by a discrete single film or layer having certain characteristics or multiple films or layers, and a boundary between adjacent films or layers may or may not be clear and may be established based on physical, chemical, and/or any other characteristics, formation processes or sequence, and/or functions or purposes of the adjacent films or layers.

In this disclosure, “containing a Si—N bond” may refer to being characterized by a Si—N bond or Si—N bonds, having a main skeleton substantially constituted by a Si—N bond or Si—N bonds, and/or having a substituent substantially constituted by a Si—N bond or Si—N bonds. A dielectric film containing a Si—N bond includes, but is not limited to, a SiN film and a SiON film, which have a dielectric constant of about 2 to 10, typically about 4 to 8.

In this disclosure, “annealing” refers to a process during which a material is treated to get into its stable form, e.g., a terminal group (such as an alcohol group and hydroxyl group) present in a component is replaced with a more stable group (such as a Si-Me group) and/or forms a more stable form (such as a Si—O bond), typically causing densification of a film.

Further, in this disclosure, the article “a” or “an” refers to a species or a genus including multiple species unless specified otherwise. The terms “constituted by” and “having” refer independently to “typically or broadly comprising”, “comprising”, “consisting essentially of”, or “consisting of” in some embodiments. Also, in this disclosure, any defined meanings do not necessarily exclude ordinary and customary meanings in some embodiments.

Additionally, in this disclosure, any two numbers of a variable can constitute a workable range of the variable as the workable range can be determined based on routine work, and any ranges indicated may include or exclude the endpoints. Additionally, any values of variables indicated (regardless of whether they are indicated with “about” or not) may refer to precise values or approximate values and include equivalents, and may refer to average, median, representative, majority, etc. in some embodiments.

In the present disclosure where conditions and/or structures are not specified, the skilled artisan in the art can readily provide such conditions and/or structures, in view of the present disclosure, as a matter of routine experimentation. In all of the disclosed embodiments, any element used in an embodiment can be replaced with any elements equivalent thereto, including those explicitly, necessarily, or inherently disclosed herein, for the intended purposes. Further, the present invention can equally be applied to apparatuses and methods.

The embodiments will be explained with respect to preferred embodiments in various aspects. However, the present invention is not limited to the preferred embodiments.

Some embodiments provide a method for fabricating a layer structure constituted by a dielectric film containing a Si—N bond in a trench formed in an upper surface of a substrate, comprising: (i) simultaneously forming a dielectric film containing a Si—N bond on the upper surface, and a bottom surface and sidewalls of the trench, wherein a top/bottom portion of the dielectric film formed on the upper surface and the bottom surface and a sidewall portion of the dielectric film formed on the sidewalls are given different chemical resistance properties by bombardment of a plasma excited by applying voltage between two electrodes between which the substrate is place in parallel to the two electrodes; and (ii) substantially removing either one of but not both of the top/bottom portion and the sidewall portion of the dielectric film by wet etching which removes the one of the top/bottom portion and the sidewall portion of the dielectric film more predominantly than the other according to the different chemical resistance properties. The term “simultaneously forming” may refer to forming generally or substantially at the same time, in the same process, or in the same step, which includes depositing generally or substantially at the same time, in the same process, or in the same step, and/or treating generally or substantially at the same time, in the same process, or in the same step. In this disclosure, the term “substantial” or “substantially” may refer to ample, considerable, or material quantity, size, time, or space (e.g., at least 70%, 80%, 90%, or 95% relative to the total or referenced value) recognized by a skilled artisan in the art to be sufficient for the intended purposes or functions.

FIG. 2 is a flowchart illustrating steps of fabricating a layer structure according to an embodiment of the present invention. Step S1 and step S2 correspond to steps (i) and (ii), respectively. In step S1, by using plasma bombardment, a dielectric film having directionality of film properties is formed over a trench. The plasma bombardment can be applied during the deposition of the film or after the completion of deposition of the film. In step S2, according to the difference in the film properties between the top/bottom portion of the film and the sidewall portion of the film, one of the portions of the film is more predominantly etched than the other by wet etching, leaving only one of the portions in the layer structure.

In step S2, the wet etching is conducted using a solution of hydrogen fluoride (HF), for example.

By adjusting bombardment of a plasma excited by applying voltage between two electrodes between which the substrate is place in parallel to the two electrodes, a top/bottom portion of the dielectric film formed on the upper surface and the bottom surface and a sidewall portion of the dielectric film formed on the sidewalls can be given different chemical resistance properties. A plasma is a partially ionized gas with high free electron content (about 50%), and when a plasma is excited by applying AC voltage between parallel electrodes, ions are accelerated by a self dc bias (V_(DC)) developed between plasma sheath and the lower electrode and bombard a film on a substrate placed on the lower electrode in a direction perpendicular to the film (the ion incident direction). The bombardment of a plasma can be represented by plasma density or kinetic energy of ions. The plasma density can be modulated mainly by tuning the pressure and RF power (the lower the pressure and the higher the power, the higher the plasma density becomes). The plasma density can also be modulated by applying a dc bias voltage or an AC voltage with a lower frequency set for ions to follow (<1 MHz). The plasma density can be determined using a probe method (e.g., “High accuracy plasma density measurement using hybrid Langmuir probe and microwave interferometer method”, Deline C, et al., Rev. Sci. Instrum. 2007 November; 78(11): 113504, the disclosure of which is incorporated by reference in its entirety). When inserting a probe in a plasma and applying a voltage thereto, an electric current flows through the probe, which is called “ion saturation current” (I_(i)) which can be calculated as follows, and then the plasma density (N_(p)) can be calculated as follows:

I_(i)=e×N_(e)√(kT_(e)/M)×exp(½)eA; N_(p)=I_(i)√(M/kT_(e))/exp(½)eA, wherein I_(i): ion saturation current [A]; A: surface area of the probe [m²]; e: electronic charge [C]; Ne: electron density [m⁻³]; k: Boltzmann's constant [J/K]; T_(e): electron temperature [K]; M: ion mass [kg].

FIG. 14 is a graph showing a general relationship between plasma density and wet etch rate of a film formed on a top surface and that of a film formed on sidewalls of a trench according to an embodiment of the present invention. In this graph, the chemical resistance properties are represented by wet etch rate. On the top/bottom surface of the film, plasma bombardment is exerted generally in a direction perpendicular to the film surface, whereas on the sidewall surface of the film, plasma bombardment is exerted generally in a direction parallel to the film surface. The wet etch rate of a film formed on the top/bottom surfaces of a trench is low when the plasma density is low since ions included in the plasma exerted on the film remove impurities and cause densification of the film. However, the wet etch rate of the film formed on the top/bottom surfaces increases as the plasma density increases as shown in FIG. 14, because the dose of ions is so high as to enhance dissociation of Si—N bond. On the other hand, the wet etch rate of a film formed on the sidewall surfaces of the trench is high when the plasma density is low since the dose of ions included in the plasma exerted on the film is insufficient to remove impurities and to cause densification of the film. However, the wet etch rate of the film formed on the sidewall surfaces decreases as the plasma density increases as shown in FIG. 14. In other words, the film quality of the film formed on the top/bottom surfaces is degraded as the plasma density increases, whereas the film quality of the film formed on the sidewall surface is improved as the plasma density increases. Thus, there is a threshold point in the plasma density where the film quality (or film characteristics) of the film on the top/bottom surfaces and that of the film on the sidewall are substantially equivalent, i.e., the line showing the relationship between plasma density and the wet etch rate of the film formed on the top/bottom surfaces and that of the film formed on the sidewalls intersect at the threshold point as shown in FIG. 14. The film characteristics of the film on the top/bottom surfaces and that of the film on the sidewall surface are reversed at the threshold point. Accordingly, by adjusting the plasma density, the film having directionality of film properties can be formed. When the plasma density is set to be lower than the threshold point, the film on the sidewalls can be more predominantly removed than is the film on the top/bottom surfaces by wet etching, whereas when the plasma density is set to be higher than the threshold point, the film on the top/bottom surfaces can be more predominantly removed than is the film on the sidewalls by wet etching. Accordingly, a desired layer structure can be fabricated.

In FIG. 14, the intersecting point (threshold point) is changed according to the duration of application of voltage, the frequency, the pressure, the distance between the electrodes, the temperature, etc., wherein, generally, the longer the duration of application of voltage, and the lower the pressure, the lower the plasma density at the intersecting point becomes. It should be noted that when the pressure, RF power, voltage, etc. are constant, a relationship substantially similar to that shown in FIG. 14 can be obtained between wet etch rate and RF power between parallel electrodes. The threshold point can be determined prior to steps (i) and (ii) based on this disclosure and routine experimentation. Thus, in some embodiments, the method for fabricating a layer structure further comprises, prior to steps (i) and (ii), repeating the following steps to determine the threshold point (reference point): (a) simultaneously forming a dielectric film under the same conditions as in step (i) except that the voltage is changed as a variable; and (b) substantially removing either one of but not both of the top/bottom portion and the sidewall portion of the dielectric film by wet etching under the same conditions as in step (ii).

FIG. 3 is a flowchart illustrating steps of fabricating a layer structure according to an embodiment of the present invention. Step S11 corresponds to steps (a) and (b), and steps S12 and S13 correspond to steps (i) and (ii), respectively. In step S11, the threshold voltage for plasma bombardment for reversing film characteristics of a top/bottom portion and a sidewall portion of a film is determined. In step S12, by using plasma bombardment at a voltage adjusted with reference to the determined threshold voltage, a dielectric film having directionality of film properties is formed over a trench. For example, when a voltage higher than the threshold voltage is applied between the electrodes in step S12, the wet etch rate of the top/bottom portion of the film becomes higher than that of the sidewall portion of the film, resulting in predominantly removing the top/bottom portion of the film, rather than the sidewall portion of the film by wet etching in step S13. On the other hand, when a voltage lower than the threshold voltage is applied between the electrodes in step S12, the wet etch rate of the sidewall portion of the film becomes higher than that of the top/bottom portion of the film, resulting in predominantly removing the sidewall portion of the film, rather than the top/bottom portion of the film by wet etching in step S13.

When ion bombardment is exerted on a film without using a parallel electrode configuration, e.g., by using a reactant in low-pressure chemical vapor deposition (LPCVD), a threshold point such as that shown in FIG. 14 would not be obtained since the reactant in LPCVD does not create asymmetrical ion bombardment, i.e., does not create directionality of film properties. For example, United States Patent Application Publication No. 2003/0029839 discloses LPCVD in which nitrogen-containing ions such as N₂ ⁺ are implanted to form a nitrogen-enriched layer, followed by thermal annealing to promote Si—N and N—H bonds in the layer so as to reduce the wet etch rate of the layer. In contrast, in some embodiments of the present invention, asymmetrical plasma bombardment using nitrogen is exerted on a top/bottom layer, which does not enrich nitrogen in the layer, but dissociates Si—N bonds and reduces the density of the layer, thereby increasing the wet etch rate of the layer formed on the top/bottom surfaces, relative to the wet etch rate of the layer formed on the sidewalls of a trench. In the above, when Si—N bonds are dissociated, Si dangling bonds and N dangling bonds are formed, which are ultimately terminated by hydrogen, forming N—H bonds and Si—H bonds. As a result of dissociating Si—N bonds, the density of the layer is decreased, and the wet etch rate is increased. Thus, in some embodiments, no thermal annealing (such as at 900° C.) is conducted between steps (i) and (ii) in order to avoid densification of the top/bottom layer (i.e., to avoid reducing the wet etch rate of the top/bottom layer). Further, in some embodiments, the incident energy of ions is less than approximately 200 eV (plasma potential is approximately 100 to 200 V), which is lower than that disclosed in United States Patent Application Publication No. 2003/0029839 (0.5 to 20 keV). As with the reactant in LPCVD, a reactant in thermal atomic layer deposition (ALD) and a plasma of remote plasma deposition do not form a threshold point such as that shown in FIG. 14 since the plasmas of thermal ALD and remote plasma deposition also do not create asymmetrical ion bombardment, i.e., do not create directionality of film properties. Further, when a plasma such as surface wave plasma (SWP) having low electron temperature and low ion kinetic energy of incident ions is used, the effect of ion bombardment is very limited, and thus, film degradation does not occur, and thus, it is difficult to create directionality of film properties. Furthermore, even when plasma bombardment is exerted on a film constituted by silicon oxide, the film quality of the silicon oxide film is not degraded, and thus, it is difficult to create directionality of film properties.

In some embodiments, the plasma is a capacitively coupled plasma (CCP) which is excited by applying RF power to one of the two electrodes. Further, in some embodiments, inductively coupled plasma (ICP), electron cyclotron resonance (ECR) plasma, microwave surface wave plasma, helicon wave plasma, etc. can be used as the plasma, wherein bias voltage is applied to the electrodes as necessary to increase dc bias voltage between the plasma and electrode.

In some embodiments, the RF power is higher than the reference RF power at which the chemical resistance properties of the top/bottom portion of the dielectric film and the sidewall portion of the dielectric film are substantially equivalent, wherein the wet etching removes the top/bottom portion of the dielectric film selectively relative to the sidewall portion of the dielectric film.

In some embodiments, the plasma is a plasma of Ar, N₂, and/or O₂ or other atoms which have an atomic number higher than hydrogen or helium.

In some embodiments, the trench has a width of 10 to 50 nm (typically 15 to 30 nm) (wherein when the trench has a length substantially the same as the width, it is referred to as a hole/via, and a diameter thereof is 10 to 50 nm), a depth of 30 to 200 nm (typically 50 to 150 nm), and an aspect ratio of 3 to 20 (typically 3 to 10).

In some embodiments, the dielectric film can be used as an etching stopper, low-k spacer, or gap-filler. For example, when only the sidewall portion is left, the portion can be used as a spacer for spacer-defined double patterning (SDDP), or when only the top/bottom portion is left, the portion can be used as a mask used for solid-state doping (SSD) of a sidewall layer exclusively.

In some embodiments, step (i) comprises: (ia) placing a substrate having a trench in its upper surface between the electrodes; and (ib) depositing the dielectric film on the substrate by plasma-enhanced atomic layer deposition (PEALD) using nitrogen gas as a reactant gas, wherein the plasma is a capacitively coupled plasma (CCP) which is excited by applying RF power to one of the two electrodes in each cycle of the PEALD, wherein the RF power is higher than the reference RF power at which the chemical resistance properties of the top/bottom portion of the dielectric film and the sidewall portion of the dielectric film are substantially equivalent so that the wet etching in step (ii) removes the top/bottom portion of the dielectric film selectively relative to the sidewall portion of the dielectric film. In the above, the film having directionality of film properties is formed as the film is depositing, not after the completion of deposition of the film.

FIG. 4 is a flowchart illustrating steps of fabricating a layer structure according to still another embodiment of the present invention. Step S21 corresponds to step (ib), and step S22 corresponds to step (ii). In step S21, a dielectric film having directionality of film properties is deposited over a trench by using plasma bombardment at a voltage higher than the threshold voltage, and in step S22, a top/bottom portion of the film is more predominantly removed than is a sidewall portion of the film, so that substantially only the sidewall portion is left in the layer structure.

In some embodiments, step (i) comprises: (ia) placing a substrate having a trench on its upper surface between the electrodes; and (ic) depositing the dielectric film on the substrate by plasma-enhanced atomic layer deposition (PEALD) using nitrogen gas as a reactant gas, wherein the plasma is a capacitively coupled plasma (CCP) which is excited by applying RF power to one of the two electrodes in each cycle of the PEALD, wherein the RF power is lower than reference RF power at which the chemical resistance properties of the top/bottom portion of the dielectric film and the sidewall portion of the dielectric film are substantially equivalent so that the wet etching in step (ii) removes the sidewall portion of the dielectric film selectively relative to the top/bottom portion of the dielectric film. In the above, the film having directionality of film properties is formed as the film is depositing, not after the completion of deposition of the film.

FIG. 5 is a flowchart illustrating steps of fabricating a layer structure according to yet another embodiment of the present invention. Step S31 corresponds to step (ic), and step S32 corresponds to step (ii). In step S31, a dielectric film having directionality of film properties is deposited over a trench by using plasma bombardment at a voltage lower than the threshold voltage, and in step S32, a sidewall portion of the film is more predominantly removed than is a top/bottom portion of the film, so that substantially only the top/bottom portion is left in the layer structure.

In some embodiments, the dielectric film is SiN film or SiON film or other Si—N bond-containing film.

In some embodiments, the PEALD or other deposition methods uses one or more compounds selected from the group consisting of aminosilane, halogenated silane, monosilane, and disilane as a precursor. The aminosilane and halogenated silane include, but are not limited to, Si₂Cl₆, SiCl₂H₂, SiI₂H₂, bisdiethylaminosilane, bisdimethylaminosilane, hexaethylaminodisilane, tetraethylaminosilane, tart-butylamonosilane, bistart-butylamonosilane, trimehylsilyldiethylamine, trimethysilyldiethylamine, and bisdimethylaminodimethylsilane.

In some embodiments, step (i) comprises: (iA) depositing a dielectric film on a substrate having a trench in its upper surface; (iB) placing the substrate between the two electrodes; and (iC) exciting the plasma between the electrodes to treat a surface of the deposited dielectric film without depositing a film, wherein the plasma is a capacitively coupled plasma (CCP) which is excited by applying RF power to one of the two electrodes, wherein the RF power is higher than the reference RF power at which the chemical resistance properties of the top/bottom portion of the dielectric film and the sidewall portion of the dielectric film are substantially equivalent so that the wet etching in step (ii) removes the top/bottom portion of the dielectric film selectively relative to the sidewall portion of the dielectric film. In the above, the film having directionality of film properties is formed after completion of deposition of a film, by treating the film. In the above, step (ii) is post-deposition treatment which need not be cyclic.

FIG. 6 is a flowchart illustrating steps of fabricating a layer structure according to a different embodiment of the present invention. Step S41 corresponds to step (iA), step S42 corresponds to steps (iB) and (iC), and step S43 corresponds to step (ii). In step S41, a dielectric film is deposited over a trench, which film need not have directionality of film properties, although it can already possess directionality of film properties. In step S42, plasma bombardment as post-deposition treatment is exerted on the film at a voltage higher than the threshold voltage so that the wet etch rate of a top/bottom portion of the film is higher than that of a sidewall portion of the film. In step S43, the top/bottom portion of the film is more predominantly removed than is the sidewall portion of the film by wet etching, so that substantially only the sidewall portion of the film is left in the layer structure. Since the film is already deposited before the post-deposition treatment, the use of a voltage lower than the threshold voltage may not be effective because the wet etch rate of the sidewall portion does not become higher than that of the as-deposited film by exerting plasma bombardment on the film as illustrated in FIG. 14 discussed above.

In some embodiments, the deposited dielectric film has a thickness of approximately 10 nm or less (typically approximately 5 nm or less). If the film to be treated is thicker than approximately 10 nm, plasma bombardment does not reach a bottom of the film, i.e., it is difficult to adjust the wet etch rate of the film entirely in the thickness direction.

The dielectric film subjected to the post-deposition treatment can be deposited on the substrate by any suitable deposition methods including plasma-enhanced atomic layer deposition (PEALD), thermal ALD, low-pressure chemical vapor deposition (PCVD), remote plasma deposition, PECVD, etc. Preferably, the dielectric film is deposited by ALD since ALD can provide a high conformality such as more than approximately 70% (or more than 80% or 90%).

In some embodiments, no annealing is conducted after depositing the dielectric film and before step (ii).

In some embodiments, the deposition cycle may be performed by PEALD, one cycle of which is conducted under conditions shown in Table 1 below.

TABLE 1 (numbers are approximate) Conditions for Deposition Cycle Substrate 100 to 600° C. (preferably temperature 250 to 550° C.) Pressure 10 to 2000 Pa (preferably 100 to 800 Pa) Precursor SiI₂H₂, etc. Precursor pulse 0.05 to 10 sec (preferably 0.2 to 1 sec) Precursor purge 0.05 to 10 sec (preferably 0.2 to 3 sec) Reactant N₂ + H₂ mixture, or NH₃ + N₂ mixture Flow rate of 100 to 20000 sccm (preferably reactant 1000 to 3000 sccm) for N₂; (continuous) 0 to 6000 sccm (preferably 0 to 600 sccm) for H₂ or NH₃ (H₂/N₂ = 0-0.5, preferably 0-0.2) Flow rate of carrier 100 to 5000 sccm (preferably 1000 gas (continuous) to 3000 sccm) Ar or N₂ Flow rate of dilution 0 to 10000 sccm (preferably gas (continuous) 0 to 5000 sccm) Ar or N₂ RF power Less than 600 W (preferably (13.56 MHz) for a 100 to 500 W) for WER 300-mm wafer of sidewall being higher than WER of top/bottom; 600 W or more (preferably 600 to 1000 W) for WER of top/bottom being higher than WER of sidewall RF power pulse 0.05 to 30 sec (preferably 1 to 5 sec) Purge 0.05 to 10 sec (preferably 0.2 to 3 sec) Growth rate per cycle 0.02 to 0.06 nm/cycle (on top surface) Step coverage (side/top; 20 to 100%; 30 to side/bottom) 100% (preferably, 50 to 100%; 50 to 100%) Distance between 5 to 30 mm (preferably electrodes 7 to 20 mm)

In some embodiments, the post-deposition treatment may be performed under conditions shown in Table 2 below.

TABLE 2 (numbers are approximate) Conditions for Post-Deposition Treatment Thickness of SiN film 2 to 15 nm (preferably 5 to 10 nm) Substrate temperature 25 to 600° C. (preferably 100 to 500° C.) Pressure 10 to 2000 Pa (preferably 100 to 500 Pa) Reactant N₂, H₂, NH₃ Flow rate 100 to 20000 sccm (preferably of reactant 1000 to 3000 sccm) for N₂; (continuous) 0 to 6000 sccm (preferably 0 to 600 sccm) for H₂ or NH₃ (H₂/N₂ = 0-0.5, preferably 0-0.2) Flow rate of carrier gas 100 to 5000 sccm (preferably (continuous) 1000 to 3000 sccm) Ar or N₂ Flow rate of dilution gas 0 to 10000 sccm (preferably (continuous) 0 to 5000 sccm) Ar or N₂ RF power (13.56 MHz) for a More than 600 W (preferably 300-mm wafer 600 to 1000 W) Duration of RF power 1 to 600 sec. (preferably application 30 to 180 sec.) Distance between electrodes 5 to 30 mm (preferably 7 to 20 mm)

In the above, although no precursor is fed to the reaction chamber, and a carrier gas flows continuously.

In some embodiments, wet etching may be performed under conditions shown in Table 3 below.

TABLE 3 (numbers are approximate) Conditions for Wet etching Etching solution HF 0.05-5% Etching solution 10 to 50° C. (preferably 15 to 30° C.) temperature Duration of etching 1 sec to 5 min (preferably 1 to 3 min) Etching rate 0.1 to 5 nm/min (preferably 0.5 to 2 nm/min)

For wet etching, any suitable single-wafer type or batch type apparatus including any conventional apparatuses can be used. Also, any suitable solution for wet etching including any conventional solutions can be used.

In some embodiments, in place of wet etching, any other suitable etching such as dry etching or plasma etching can be conducted. A skilled artisan can readily determined the etching conditions such as temperature, duration, etchant concentration, as routine experimentation in view of this disclosure.

In some embodiments, an insulation film can be formed only on a sidewall of a trench as follows:

1) forming a SiN film over a substrate having a trench pattern, in which a pulse of feeding a precursor and a pulse of exposing the substrate to an ambient atmosphere containing nitrogen species excited by a plasma are repeated, in which the plasma is excited in a manner exerting plasma bombardment on the substrate in a direction perpendicular to the substrate (the incident angle of ions is perpendicular to the substrate) under conditions such that the wet etch rate of a sidewall portion of the film is lower than that of a top/bottom portion of the film; and

2) removing the top/bottom portion of the film by wet etching.

In the above process sequence, the precursor is supplied in a pulse using a carrier gas which is continuously supplied. This can be accomplished using a flow-pass system (FPS) wherein a carrier gas line is provided with a detour line having a precursor reservoir (bottle), and the main line and the detour line are switched, wherein when only a carrier gas is intended to be fed to a reaction chamber, the detour line is closed, whereas when both the carrier gas and a precursor gas are intended to be fed to the reaction chamber, the main line is closed and the carrier gas flows through the detour line and flows out from the bottle together with the precursor gas. In this way, the carrier gas can continuously flow into the reaction chamber, and can carry the precursor gas in pulses by switching the main line and the detour line. FIG. 1B illustrates a precursor supply system using a flow-pass system (FPS) according to an embodiment of the present invention (black valves indicate that the valves are closed). As shown in (a) in FIG. 1B, when feeding a precursor to a reaction chamber (not shown), first, a carrier gas such as Ar (or He) flows through a gas line with valves b and c, and then enters a bottle (reservoir) 30. The carrier gas flows out from the bottle 30 while carrying a precursor gas in an amount corresponding to a vapor pressure inside the bottle 30, and flows through a gas line with valves f and e, and is then fed to the reaction chamber together with the precursor. In the above, valves a and d are closed. When feeding only the carrier gas (noble gas) to the reaction chamber, as shown in (b) in FIG. 1B, the carrier gas flows through the gas line with the valve a while bypassing the bottle 30. In the above, valves b, c, d, e, and f are closed.

The precursor may be provided with the aid of a carrier gas. Since ALD is a self-limiting adsorption reaction process, the number of deposited precursor molecules is determined by the number of reactive surface sites and is independent of precursor exposure after saturation, and a supply of the precursor is such that the reactive surface sites are saturated thereby per cycle. A plasma for deposition may be generated in situ, for example, in an ammonia gas that flows continuously throughout the deposition cycle. In other embodiments the plasma may be generated remotely and provided to the reaction chamber.

As mentioned above, each pulse or phase of each deposition cycle is preferably self-limiting. An excess of reactants is supplied in each phase to saturate the susceptible structure surfaces. Surface saturation ensures reactant occupation of all available reactive sites (subject, for example, to physical size or “steric hindrance” restraints) and thus ensures excellent step coverage. In some embodiments the pulse time of one or more of the reactants can be reduced such that complete saturation is not achieved and less than a monolayer is adsorbed on the substrate surface.

The process cycle can be performed using any suitable apparatus including an apparatus illustrated in FIG. 1A, for example. FIG. 1A is a schematic view of a PEALD apparatus, desirably in conjunction with controls programmed to conduct the sequences described below, usable in some embodiments of the present invention. In this figure, by providing a pair of electrically conductive flat-plate electrodes 4, 2 in parallel and facing each other in the interior 11 (reaction zone) of a reaction chamber 3, applying HRF power (13.56 MHz or 27 MHz) 20 to one side, and electrically grounding the other side 12, a plasma is excited between the electrodes. A temperature regulator is provided in a lower stage 2 (the lower electrode), and a temperature of a substrate 1 placed thereon is kept constant at a given temperature. The upper electrode 4 serves as a shower plate as well, and reactant gas (and noble gas) and precursor gas are introduced into the reaction chamber 3 through a gas line 21 and a gas line 22, respectively, and through the shower plate 4. Additionally, in the reaction chamber 3, a circular duct 13 with an exhaust line 7 is provided, through which gas in the interior 11 of the reaction chamber 3 is exhausted. Additionally, a dilution gas is introduced into the reaction chamber 3 through a gas line 23. Further, a transfer chamber 5 disposed below the reaction chamber 3 is provided with a seal gas line 24 to introduce seal gas into the interior 11 of the reaction chamber 3 via the interior 16 (transfer zone) of the transfer chamber 5 wherein a separation plate 14 for separating the reaction zone and the transfer zone is provided (a gate valve through which a wafer is transferred into or from the transfer chamber 5 is omitted from this figure). The transfer chamber is also provided with an exhaust line 6. In some embodiments, the deposition of multi-element film and surface treatment are performed in the same reaction space, so that all the steps can continuously be conducted without exposing the substrate to air or other oxygen-containing atmosphere. In some embodiments, a remote plasma unit can be used for exciting a gas.

In some embodiments, in the apparatus depicted in FIG. 1A, the system of switching flow of an inactive gas and flow of a precursor gas illustrated in FIG. 1B (described earlier) can be used to introduce the precursor gas in pulses without substantially fluctuating pressure of the reaction chamber.

In some embodiments, a dual chamber reactor (two sections or compartments for processing wafers disposed close to each other) can be used, wherein a reactant gas and a noble gas can be supplied through a shared line whereas a precursor gas is supplied through unshared lines.

A skilled artisan will appreciate that the apparatus includes one or more controller(s) (not shown) programmed or otherwise configured to cause the deposition and reactor cleaning processes described elsewhere herein to be conducted. The controller(s) are communicated with the various power sources, heating systems, pumps, robotics, and gas flow controllers or valves of the reactor, as will be appreciated by the skilled artisan.

The present invention is further explained with reference to working examples below. However, the examples are not intended to limit the present invention. In the examples where conditions and/or structures are not specified, the skilled artisan in the art can readily provide such conditions and/or structures, in view of the present disclosure, as a matter of routine experimentation. Also, the numbers applied in the specific examples can be modified by a range of at least ±50% in some embodiments, and the numbers are approximate.

In some embodiments, an insulation film can be formed only on a sidewall of a trench as follows:

1) forming a SiN film over a substrate having a trench pattern (the film may or may not have directionality of film properties);

2) treating the film with a plasma excited in a manner exerting plasma bombardment on the substrate in a direction perpendicular to the substrate (the incident angle of ions is perpendicular to the substrate) under conditions such that the wet etch rate of a sidewall portion of the film is lower than that of a top/bottom portion of the film; and

3) removing the top/bottom portion of the film by wet etching.

Application to SDDP or Other Patterning

In microfabrication or miniaturization of semiconductor devices, pattern transfer and target etching using spacer-defined double patterning (SDDP) is essential technology. The typical steps of SDDP basically comprises: (i) forming a resist pattern, (ii) transferring the pattern to a hard mask, (iii) forming a pattern transfer film covering the entire surface, followed by etch back to expose a top of the patterned hard mask and an underlying layer while leaving the patterned hard mask as a core material and a vertical portion of the pattern transfer film as a vertical spacer, and (iv) removing the core material and etching the underlying layer using the vertical spacer as a mask. However, conventional SDDP faces a problem that the number of steps is high, and it is difficult to perform uniform and conformal patterning.

In conventional SDDP, a SiO film is used as a pattern transfer film deposited on a core hard mask (CHM), which is subjected to etch back. FIG. 15 is a SEM photograph showing a cross sectional view of a vertical spacer constituted by the SiO film after the etch back. As shown in FIG. 15, the vertical spacer 62 constituted by SiO film formed on a Si substrate 61 has clearly sloped shoulders 63, i.e., a top part of the vertical spacer is tapered and sloped, and thus, it is difficult to use the SiO film as the pattern transfer film in SDDP.

In some embodiments, the shape of the shoulders of the vertical spacer is controlled by adjusting resistance to dry etching of a pattern transfer film when being deposited on a template. The pattern transfer film can be constituted by any of the SiN films disclosed herein.

FIG. 17 illustrates cross-sectional views of a silicon nitride film, wherein (a) illustrates high-ion dose areas in dark gray when the film is deposited for SDDP, (b) illustrates ion irradiation areas in dark gray when the film is subjected to dry etching, and (c) illustrates an etched structure according to an embodiment of the present invention. In (a), a pattern transfer film (73 a, 73 b, 73 c) constituted by SiN is deposited on a mandrel or core pattern 72 (core hard mask, CHM) and an underlying layer 71. In the pattern transfer film, portions deposited on a flat or horizontal surface, i.e., a bottom portion 73 a and a top portion 73 c, receive a higher ion dose than does a portion deposited on a vertical surface, i.e., a sidewall portion 73 b, since the horizontal portions receive more ion bombardment by a plasma generated by RF power than that of the vertical portion. More specifically, considering a virtual boundary 74 between the top portion 73 c and the sidewall portion 73 b in (a), an inner area thereof receives a higher ion dose than that of an outer area thereof because ions rather anisotropically bombards and penetrates the film while being deposited, and the inner area is exposed to the ion bombardment longer than is the outer area, and thus, the virtual boundary 74 is upwardly inclined from the inside to the outside as illustrated in (a).

Typically, the DER property of a SiN film deposited by PEALD according to the embodiments disclosed herein has RF power dependency. That is, RF power used for depositing the SiN film defines ion dose to which the SiN film is exposed when the film is deposited, and the higher the ion dose, the higher the DER property (i.e., the higher the damage of the film) becomes. Because the higher the ion dose, the higher the DER property becomes, the DER property of the bottom and top portions 73 a, 73 c is higher than that of the sidewall portion 73 b, and a virtual boundary therebetween corresponds to the virtual boundary 74 as illustrated in (a).

On the other hand, when the film is subjected to dry etching in (b), a bottom portion 73 a′ and a top portion 73 c′ receive higher ion irradiation than does a sidewall portion 73 b′, since the horizontal portions receive more ion irradiation by anisotropic dry etching (e.g., reactive ion etch (ME)) than that of the vertical portion. More specifically, considering a virtual boundary 74′ between the top portion 73 c′ and the sidewall portion 73 b′ in (b), because the exposed surface and the horizontal portion receive high ion irradiation and etching progresses downwardly while being anisotropically etched, the virtual boundary 74′ is downwardly inclined from the inside to the outside as illustrated in (b), particularly when the top edges are rounded. Because the higher the ion irradiation, the higher the DER of the film becomes, the DER of the bottom and top portions 73 a′, 73 c′ is higher than that of the sidewall portion 73 b′, and a virtual boundary therebetween corresponds to the virtual boundary 74′ as illustrated in (b) (as sloped shoulders).

In the above, since the virtual boundary 74 of the top portion 73 c (the high ion dose area) having high-DER property is inclined in a direction opposite to that of the virtual boundary 74′ of the top portion 73 c′ (the ion irradiation area) having high DER, when dry etching of the film is actually conducted until the top of the mandrel 72 and the top surface of the underlying layer 71 are exposed, a top edge 74″ of a sidewall portion 73 b″ can become substantially flat as illustrated in (c) in FIG. 17, effectively avoiding formation of a sloped shoulder. By adjusting the virtual boundaries 74 and 74′ using process parameters (e.g., process gas, pressure, temperature, RF power, etc.), the differences in properties between the inner area and the outer area of the film when being dry-etched can be substantially offset by the differences in properties between the inner area and the outer area of the film when being deposited, so that the top edge of the sidewall portion (vertical spacer) can be substantially flat without forming a sloped shoulder. For example, “substantially flat” refers to flat to the extent that spacer-defined quadruple patterning (SDQP) can be performed using the spacer.

The SiN film disclosed herein can be used in various applications, including spacer-defined double patterning (SDDP). FIG. 19 is a schematic representation of pattern transfer and target etching using SDDP according to an embodiment of the present invention, wherein a SiN film is used as a pattern transfer film to transfer a pattern from a first template to a second template. An antireflective layer (ARL) 94 is used as the first template for increasing pattern density (e.g., pitch reduction) in SDDP processes. An etch hardmask 82 is used as the second template for etching a target layer 81. In step (a) in FIG. 19, on the antireflective layer 94 (constituted by e.g., amorphous carbon), a photoresist pattern 93 (constituted by e.g., Novolacs) is formed so that the antireflective layer 94 can be etched in the photoresist pattern in step (b) which is a step of transferring a pattern to the first template 94. In step (c), a SiN film 95 (as a pattern transfer film) is deposited according to any of the disclosed embodiments or equivalents thereto, followed by etching in step (d) which is a spacer RIE (reactive ion etch) step. By stripping the material of the antireflective layer 94 (a photoresist material in the core portions 96), vertical spacers 84 are formed in step (e). Since the SiN film 95 has high etch selectivity, the antireflective layer 94 (the first template) for forming the spacer thereon can be thin and the SiN film can be sustained during etching to form the vertical spacers 84 (SiN spacer) in step (e). In some embodiments, the thickness of the antireflective layer is about 5 to 50 nm (typically 10 to 30 nm), and the thickness of the SiN film is about 5 to 50 nm (typically 10 to 20 nm). In step (f), the pattern is transferred by etching from the vertical spacers 84 to the second template 82 to form second vertical spacers 74, and in step (g), the first vertical spacers 84 are stripped. Since the top edge of the SiN spacer 84 is flat, formation of the second template 82 with the second vertical spacers 74 can be accurately accomplished. In step (h), a target layer 81 formed on a silicon substrate 70 is subjected to dry etch using the second vertical spacers 74. In step (i), the second vertical spacers 74 are stripped. In some embodiments, the antireflective layer, etch hardmask, SiN film (spacer), and target layer may be deposited by any of the methods disclosed herein or equivalents thereof or by pulsed PECVD or PEALD.

The SiN film is resistant to not only HF, HCl, and TMAH wet etch, but also e.g. to BCl₃, BCl₃/Ar, dry etch, and thus, in step (f), when transferring the pattern to the second template 82, the SiN 84 sustains the pattern. On the other hand, the SiN film is sensitive to oxidation, a combination of wet etch chemistry alternating oxidizing and HF (common in semiconductor processing), or dry etch based on oxygen or CF₄, for example, and thus, in step (g), the SiN spacer 84 can effectively be stripped.

FIG. 20 is a schematic representation of double patterning (steps (a) to (c)) and quadruple patterning (steps (c) to (e)) according to an embodiment of the present invention. Since the top edge of the SiN spacer is substantially flat, the spacer can effectively and suitably be applied to not only SDDP but also spacer-defined quadruple patterning (SDQP) or a higher level (spacer-defined multiple patterning, SDMP). In step (a), mandrels 101 are patterned on an underlying layer 102. In step (b), a SiN film 103 is deposited to cover the exposed surfaces of the mandrels 101 and the exposed surface of the underlying surface 102 in their entirety. In step (c), by dry etching, the horizontal portions of the SiN film 103 and the mandrels 101 are etched so as to form vertical spacers 104 which can effectively and suitably used for SDDP. For SDQP, using the template illustrated in step (c), step (d) is performed. In step (d), another SiN film 105 is deposited to cover the exposed surfaces of the vertical spacers 104 and the exposed surface of the underlying surface 102 in their entirety. In step (e), by dry etching, the horizontal portions of the SiN film 105 and the vertical spacers 104 are etched so as to form vertical spacers 106 which can effectively and suitably used for SDQP.

In some embodiments, the SiN film as a pattern transfer film is deposited under the conditions shown in Table 1 except that the substrate temperature is in the range of 100 to 250° C. (preferably 150 to 200° C.) (due to low thermal resistance of a mandrel), and the RF power is in the range of 50 to 1500 W (preferably 200 to 900 W) for a 300-mm substrate (for other sizes of substrate, the wattage per cm² calculated from the above can be applied).

In some embodiments, dry etching of the SiN film (etch back process) is conducted under the conditions shown in Table 4 below.

TABLE 4 (numbers are approximate) Conditions for Dry Etching Thickness of target 5 to 50 nm (preferably SiN film 10 to 20 nm) Substrate temperature 10 to 30° C. (preferably 20° C.) Pressure 1 to 30 Pa (preferably 8 Pa) Etchant gas CF₄, CHF₃, C₄F₈ Flow rate of etchant 10 to 100 sccm (preferably gas (continuous) 10 to 50 sccm) Flow rate of dilution 50 to 400 sccm (preferably gas (continuous) 100 to 200 sccm); He, Ar Secondary etchant gas O₂ (0 to 300 sccm, preferably (continuous) 10 to 100 sccm) with or without Ar (0 to 500 sccm, preferably 0 to 200 sccm) High RF power (13.56 100 to 1000 W (preferably or 27.12 MHz) for 200 to 600 W) a 300-mm wafer Low RF power (400 kHz) 0 to 500 W (preferably for a 300-mm wafer 100 to 300 W) Duration of RF power 5 to 60 sec. (preferably application 5 to 30 sec.) Distance between 10 to 50 mm electrodes (preferably 20 to 40 mm)

In the above, for other sizes of substrate, the wattage per cm² calculated from the above can be applied.

The present invention is further explained with reference to working examples below. However, the examples are not intended to limit the present invention. In the examples where conditions and/or structures are not specified, the skilled artisan in the art can readily provide such conditions and/or structures, in view of the present disclosure, as a matter of routine experimentation. Also, the numbers applied in the specific examples can be modified by a range of at least ±50% in some embodiments, and the numbers are approximate.

EXAMPLES Reference Example 1

A SiN film was formed on a Si substrate (Φ300 mm) having trenches by PEALD, one cycle of which was conducted under the conditions shown in Table 5 (deposition cycle) below using the PEALD apparatus illustrated in FIG. 1A and a gas supply system (FPS) illustrated in FIG. 1B.

After taking out the substrate from the reaction chamber, the substrate was subjected to wet etching under the conditions shown in Table 5 below.

TABLE 5 (numbers are approximate) Conditions for Deposition Cycle Substrate temperature 400° C. Pressure 350 Pa Precursor SiI₂H₂ Precursor pulse 0.3 sec Precursor purge 0.5 sec Reactant N₂ Flow rate of reactant (continuous) 2000 sccm Flow rate of carrier gas (continuous) 2000 sccm N₂ Flow rate of dilution gas (continuous) 0 sccm RF power (13.56 MHz) for a 300-mm wafer Variable (see FIG. 7) RF power pulse 3.3 sec Purge 0.1 sec Growth rate per cycle (on top surface) 0.05 nm/cycle Number of cycles (thickness of film on top 200 times (10 nm) surface) Step coverage (side/top; side/bottom) 100%; 100% Trench depth/width (nm) 100/33 (AR = about 3) Distance between electrodes 15 mm Conditions for Wet etching Etching solution 0.5% HF Etching solution temperature 20° C. Duration of etching 2 min Etching rate Variable (see FIG. 7)

The results are shown in FIG. 7. FIG. 7 is a graph showing the relationship between RF power and wet etch rate of the film formed on the top surface and that of the film formed on the sidewalls of the trench, showing a threshold (reference) RF power. As shown in FIG. 7, the wet etch rate of the sidewall portion decreased as RF power increased, whereas the wet etch rate of the top/bottom portions increased as the RF power increased, wherein the line representing the former and the line representing the latter intersect at an RF power of approximately 600 W. That is, the threshold RF power was approximately 600 W, and it can be understood that when RF power applied between the electrodes is higher than approximately 600 W, the top/bottom portions of the film can be removed selectively relative to the sidewall portion of the film, whereas when RF power applied between the electrodes is lower than approximately 600 W, the sidewall portion of the film can be removed selectively relative to the top/bottom portions of the film.

Further, prior to the wet etching, the top portion of the film was subjected to additional analyses: Si—N peak intensity and density. FIG. 12 is a graph showing the relationship between RF power and Si—N peak intensity [au] of the SiN film. FIG. 13 is a graph showing the relationship between RF power and density [g/cm³] of the SiN film. As can be seen from FIGS. 12 and 13, contrary to common technological knowledge (i.e., when increasing RF power, densification of the film occurs), asymmetrical plasma bombardment to the SiN film broke Si—N bonds when RF power increased, and as a result of dissociation of Si—N bonds, the density of the film decreased (the density is typically in a range of 2.6 to 3.2 g/cm³), wherein the density of a film portion to be removed by wet etching is lower than that of a film portion to remain through wet etching).

Reference Example 2

The SiN films were deposited under the conditions shown in Table 6, where the threshold RF power was determined to be approximately 400 W in the same manner as in Reference Example 1. The SiN films were then subjected to wet etching under the conditions shown in Table 6. FIG. 8 shows Scanning Transmission Electron Microscope (STEM) photographs of cross-sectional views of the silicon nitride films. As can be seen from FIG. 8, when RF power was 700 W, the top/bottom portions of the film were selectively removed by wet etching, and substantially no film remained (no residual film was observed) on the top surface and at the bottom of the trench. When RF power was 500 W, the top/bottom portions of the film were more predominantly removed than was the sidewall portion of the film by wet etching, but residual film remained on the top surface and at the bottom of the trench, whereas the sidewall portion of the film mostly remained. When RF power was 300 W, the sidewall portion of the film was more predominantly removed than were the top/bottom portions of the film by wet etching, and no residual film remained in some areas of the sidewall, whereas the top/bottom portions of the film mostly remained.

TABLE 6 (numbers are approximate) Conditions for Deposition Cycle Substrate temperature 200° C. Pressure 350 Pa Precursor Bisdiethylaminosilane Precursor pulse 0.2 sec Precursor purge 3 sec Reactant N₂ Flow rate of reactant (continuous) 2000 sccm Flow rate of carrier gas (continuous) 2000 sccm Ar Flow rate of dilution gas (continuous) 0 sccm RF power (13.56 MHz) for a 300-mm wafer Variable (see FIG. 8) RF power pulse 3 sec Purge 0.1 sec Growth rate per cycle (on top surface) 0.02 nm/cycle Number of cycles (thickness of film on top 500 times (10 nm) surface) Step coverage (side/top; side/bottom) 30%; 30% Trench depth/width (nm) 100/33 (AR = about 3) Distance between electrodes 13 mm Conditions for Wet etching Etching solution 0.05% HF Etching solution temperature 20° C. Duration of etching 4 min Etching rate Variable (see FIG. 8)

Reference Example 3

The SiN film was deposited in the same manner as in Example 1 except that RF power was 880 W. The SiN film was then subjected to wet etching under the same conditions as in Reference Example 1. FIG. 9 shows a Scanning Transmission Electron Microscope (STEM) photograph of a cross-sectional view of the SiN film after the wet etching. As can be seen from FIG. 9, substantially no film remained (no residual film was observed) on the top surface and at the bottom of the trench.

Reference Example 4 (Prophetic Example)

A SiN film is formed on a Si substrate (Φ300 mm) having trenches by PEALD in the same manner as in Example 1 except that RF power is 600 W. Thereafter, in the same reactor, the film is treated with a plasma under the conditions shown in Table 7 below, where RF power is 800 W which is higher than the threshold RF power, thereby causing damage to the top surface of the substrate and the bottom surface of the trench and degrading the film quality. After taking out the substrate from the reaction chamber, the substrate is subjected to wet etching under the conditions shown in Table 7 below.

TABLE 7 (numbers are approximate) Conditions for Surface treatment Substrate temperature 400° C. Pressure 350 Pa Reactant N₂ Flow rate of reactant (continuous) 2000 sccm Flow rate of carrier gas (continuous) 2000 sccm Flow rate of dilution gas (continuous) 0 sccm RF power (13.56 MHz) for a 300-mm wafer 880 W Duration of RF power application 60 sec Distance between electrodes 15 mm Conditions for Wet etching Etching solution 0.5% HF Etching solution temperature 20° C. Duration of etching 2 min Etching rate (top/sidewall) 6 nm/min, 0.2 nm/min

FIG. 10 illustrates a cross-sectional view of the silicon nitride film. Since a portion 52 of the film formed on a sidewall 51 of a trench formed in a substrate 51 does not receive substantial plasma bombardment, the portion 52 maintains film properties and remains after wet etching. In contrast, since a portion of the film formed on a top surface 51 b and a portion of the film formed on a bottom surface 51 a receive plasma bombardment, the portions degrade film properties and are removed after wet etching.

Reference Example 5 (Prophetic Example)

A SiN film is formed on a Si substrate (Φ300 mm) having trenches by PEALD, one cycle of which is conducted under the conditions shown in Table 8 (deposition cycle) below using the PEALD apparatus illustrated in FIG. 1A and a gas supply system (FPS) illustrated in FIG. 1B.

After taking out the substrate from the reaction chamber, the substrate is subjected to wet etching under the conditions shown in Table 8 below.

TABLE 8 (the numbers are approximate) Conditions for Deposition Cycle Substrate temperature 400° C. Pressure 350 Pa Precursor SiI₂H₂ Precursor pulse 0.3 sec Precursor purge 0.5 sec Reactant N₂ Flow rate of reactant (continuous) 2000 sccm Flow rate of carrier gas (continuous) 2000 sccm N₂ Flow rate of dilution gas (continuous) 0 sccm RF power (13.56 MHz) for a 300-mm wafer 100 W RF power pulse 3.3 sec Purge 0.1 sec Growth rate per cycle (on top surface) 0.05 nm/cycle Number of cycles (thickness of film on top 200 times (10 nm) surface) Trench depth/width (nm) 100/33 (AR = about 3) Step coverage (side/top; side/bottom) 100%; 100% Distance between electrodes 15 mm Conditions for Wet etching Etching solution 0.5% HF Etching solution temperature 20° C. Duration of etching 2 min Etching rate (top/sidewall) 0.3 nm/min, 2.4 nm/min

FIG. 11 illustrates a cross-sectional view of the silicon nitride films. Since RF power is 100 W which is lower than the threshold RF power (which is expected to be 600 W), a sidewall portion of the film is removed selectively relative to a top portion 53 b of the film and a bottom portion 53 a of the film by wet etching, wherein only the top/bottom portions 53 a, 53 b remain after the wet etching. This film can be used as a cap layer.

Example 1

A template was prepared by forming a core hard mask (CHM) pattern (made of amorphous carbon) using a patterned SiARC (Silicon-containing antireflection coating) on a Si substrate (Φ300 mm), wherein the patterned CHM had a height of 100 nm, a width of 25 nm, and a pitch of 100 nm. In order to determine a shape of a spacer, a SiN film was formed on the CHM pattern by PEALD, one cycle of which was conducted under the conditions shown in Table 9 (deposition cycle) below using the PEALD apparatus illustrated in FIG. 1A and a gas supply system (FPS) illustrated in FIG. 1B.

The SiN film was then subjected to an etch back process which was conducted in the same chamber, followed by stripping of the patterned CHM under the conditions shown in Table 10 below.

TABLE 9 (numbers are approximate) Conditions for Deposition Cycle Substrate temperature 180° C. Pressure 350 Pa Precursor SiI₂H₂ Precursor pulse 0.2 sec Precursor purge 3 sec Reactant N₂ Flow rate of reactant (continuous) 2000 sccm Flow rate of carrier gas (continuous) 2000 sccm Ar Flow rate of dilution gas (continuous) 0 sccm RF power (13.56 MHz) for a 300-mm wafer 248 W RF power pulse 3 sec Purge 0.1 sec Growth rate per cycle (on flat surface) 0.02 nm/cycle Number of cycles (thickness of film on top 700 times (14 nm) surface) Trench depth/width (nm) 100/100 (AR = about 1) Step coverage (side/top; side/bottom) 100%; 100% Distance between electrodes 13 mm

TABLE 10 (numbers are approximate) Conditions for Etch Back Process Substrate temperature 20° C. Pressure 8 Pa Etchant CHF₃ (10 sccm), O₂ (10 sccm), Ar (180 sccm) RF power (27.12 MHz) 300 W Duration 18 sec Conditions for Stripping Substrate temperature 20° C. Pressure 8 Pa Etchant O₂ (10 sccm), Ar (90 sccm) RF power (27.12 MHz) 300 W Duration 45 Sec

FIG. 18 shows a Scanning Electron Microscope (SEM) photograph of cross-sectional views of the SiN film deposited on the CHM pattern in (a) and spacers formed by etching the film in (b). As shown in (a) in FIG. 18, it was confirmed that the SiN film 184 was deposited to cover the CHM 182 with the convex shape SiARC 183 and the exposed surface of the Si substrate 181 with high conformality (a sidewall thickness was about 14 nm). Also, as shown in (b) in FIG. 18, it was confirmed that vertical spacers 185 were formed, which stood substantially at a right angle (about 88° to about 90° with reference to a bottom surface between adjacent spacers facing each other) with a thickness of about 12 nm, and had substantially flat top edges, indicating that even when the CHM had a rounded top, a vertical spacer with a flat top can be formed using a single SiN film deposited under same conditions, while avoiding formation of a sloped shoulder.

Reference Example 6

A SiN film was deposited on a flat silicon substrate under the conditions disclosed in Table 9 (except that RF power was changed), followed by dry etching under the conditions disclosed in Table 10.

FIG. 16 is a graph showing the relationship between deposition power and dry etching rate (DRE) of SiN film. As shown in FIG. 16, the DER of the SiN film deposited by PEALD had RF power dependency. That is, RF power used for depositing the SiN film defines ion dose to which the SiN film is exposed when the film is deposited, and the higher the ion dose, the higher the DER becomes. Since an inner area of the film receives more ion dose than does an outer area thereof, and an horizontal area of the film receives more ion dose than does a vertical area thereof, as illustrated in (a) in FIG. 17, the DER of the bottom and top portions of the 73 a, 73 c is higher than that of the sidewall portion 73 b, and a virtual boundary therebetween corresponds to the virtual boundary 74. This structure is effective to form a vertical spacer with a flat top as illustrated in (c) in FIG. 17 when being etched as illustrated in (b) in FIG. 17.

It will be understood by those of skill in the art that numerous and various modifications can be made without departing from the spirit of the present invention. Therefore, it should be clearly understood that the forms of the present invention are illustrative only and are not intended to limit the scope of the present invention. 

We claim:
 1. A method of forming spacers for spacer-defined multiple patterning (SDMP) by plasma-enhanced atomic layer deposition (PEALD) without forming sloped shoulders on top of the spacers, comprising steps of: (i) providing a template having a surface patterned by a mandrel formed on an underlying layer in a reaction space; (ii) depositing a pattern transfer film by plasma-enhanced atomic layer deposition (PEALD) on the entire patterned surface of the template using halogenated silane as a precursor and nitrogen as a reactant at a temperature of 200° C. or less using anisotropic ion bombardment by a plasma in a manner lowering film quality at a portion of the pattern transfer film formed on a top of the mandrel than film quality at a vertical portion of the pattern transfer film, wherein a boundary between the portion of the pattern transfer film on the top of the mandrel and the vertical portion of the pattern transfer film is upwardly inclined from an inner part to an outer part of the vertical portion such that in step (iii), the portion of the pattern transfer film formed on the top of the mandrel is more easily etched than the vertical portion of the pattern transfer film, said pattern transfer film being a conformal silicon nitride film and having a thickness smaller than a width of the mandrel; (iii) dry-etching the template whose entire upper surface is covered with the pattern transfer film using a fluorocarbon as an etchant by anisotropic dry etching wherein an exposed surface and a horizontal portion receive higher ion irradiation for etching than does a vertical portion so that the outer part of the vertical portion of the pattern transfer film receives higher ion irradiation than does the inner part of the vertical portion of the pattern transfer film when etching progresses, and thereby selectively removing a portion of the pattern transfer film formed on the top of the mandrel and the horizontal portion of the pattern transfer film while leaving the mandrel as a core material and the vertical portion of the pattern transfer film as a vertical spacer except for the boundary between the horizontal portion and the vertical portion wherein a top of the vertical spacer is flat to the extent that spacer-defined multiple patterning can be performed using the vertical spacer with the top; and (iv) dry-etching the core material, whereby the template has a surface patterned by the vertical spacer on the underlying layer.
 2. The method according to claim 1, wherein the mandrel is constituted by a carbon-based material.
 3. The method according to claim 1, wherein in step (ii), PEALD uses a capacitively coupled plasma (CCP) and is conducted by applying 300 W or less of RF power in the reaction space.
 4. The method according to claim 1, wherein in step (ii), the pattern transfer film has a conformality of 80% to 100%.
 5. The method according to claim 1, wherein in step (iii), the fluorocarbon is CHF₃ or CF₄.
 6. The method according to claim 1, wherein in step (iv), the core material is etched using Ar/O₂ or O₂ as an etchant.
 7. The method according to claim 1, wherein the pattern transfer film is a single silicon nitride film deposited under same conditions.
 8. The method according to claim 1, further comprising (v) dry-etching the underlying layer using the vertical spacer as a mask.
 9. The method according to claim 8, wherein SDMP is space-defined quadruple patterning (SDQP), wherein after step (iv) before step (v), steps in a depositing-etching cycle similar to steps (ii) to (iv) are repeated. 